Powell first appeared with dwarf troupes and circuses but later moved into acting and had roles in movies from the fifties onwards, his first film appearance being in Stewart Granger's Beau Brummell. He performed in many roles in his later life, including as one of the Oompa Loompas in Willy Wonka & the Chocolate Factory (1971, Mel Stuart). He was uncredited in this role, as he would be in most of his roles in the 1970s, including Star Wars. During the filming of the cantina scene in Episode IV, Powell met fellow actress Gilda Cohen, with whom he would be romantically linked.
One of the best actors of his height, Powell had a successful career in cinema and TV, including an appearance in Doctor Who in 1979 and movies such as The Elephant Man (1980, David Lynch), Time Bandits (1981, Terry Gilliam) and Top Secret! (1984, Jim Abrahams and David & Jerry Zucker; he played the little German in "I know a little German; look, there he is!"). His last movie was the thriller Killed by Inches (1999, Diane Doniol-Valcroze and Arthur Flam).
Marcus died in southern London.